Some home appliances (such as laundry washing machines and refrigerators) are today fitted with a serial communications port (or other similar output device) allowing the appliance to be connected to a personal computer which, utilising purpose built software, may interrogate information stored within the appliance. The information stored by the appliance may include the present status appliance, temperatures, status of valves/shutters, user settings, fault information and number of cycles completed.
As it is sometimes difficult or inconvenient for a service person to visit the site at which the appliance is located (which may be many kilometres from the service person's base) some existing home appliances have been fitted with modems to allow a service person to remotely interrogate data stored in the appliance. However, the additional cost involved in fitting all production appliances with a modem is unacceptably high. In addition, the user of the machine would be required to connect a telephone line to the appliance (either sharing an existing telephone line or installing a new one) and this is clearly unacceptable.
Most modern home appliances are at least fitted with a sound generating device (for example a simple piezo-electric device) to, for example, alert the user that the washing cycle of a laundry washing machine or dishwasher is completed or the door of a refrigerator is open. Accordingly, it would be an advantageous improvement to utilise the existing noise producing capability of the appliance in the production of a data signal rather than adding additional hardware.
Our earlier U.S. Pat. No. 5,987,105 describes appliances with inbuilt sound generating capability used for data communication over a standard phone network. However, the recent popularity of cell phones and other digital phone systems has brought with it several obstacles to known transmission techniques. Cell phones incorporate signal processing features such as automatic gain control, noise filtering and phase distortion. These features make achieving modem data transfer by existing methods difficult or impossible.